Overexpression of the Salmonella KdpF membrane peptide modulates expression of kdp genes and intramacrophage growth.

Membrane peptides appear as an emerging class of regulatory molecules in bacteria, which can interact with membrane proteins, including transporters and sensor kinases. The KdpF peptide, which is cotranscribed with kdpABC genes and regulated by the KdpDE two-component system, is supposed to stabilize the KdpABC potassium transporter complex but may also exhibit unsuspected regulatory function(s). The mycobacterial KdpF can interact with the KdpD histidine kinase, and kdpF overexpression has been shown to reduce intramacrophage replication of Mycobacterium bovis BCG. In this study, we investigated whether KdpF displays similar behavior in another intracellular pathogen, Salmonella enterica serovar Typhimurium. We show that Salmonella KdpF can interact with KdpD in a bacterial two-hybrid assay. We have constructed a Salmonella strain overexpressing kdpF, and we have investigated expression of the kdp regulon, as well as intramacrophage survival. We show that kdpF overexpression reduces expression of kdpA and kdpD genes under potassium limitation. Moreover, kdpF overexpression increases intramacrophage multiplication of S. Typhimurium. Hence, our results indicate that KdpF can play a regulatory role in S. Typhimurium, modulating kdp gene expression and intramacrophage survival, but in a way that differs from the one reported for M. bovis BCG.